It is known that a blade having a "twist" thereto provides more lift (and hence an increase in the displacement of air) than blades which are not so "twisted" or are uniform and consistent along their length.
The economical manner to produce aluminum fan blades is by the extrusion process, however, the extrusion process generally only produces non-twisted blades. To impart a uniform angular twist in an extruded airfoil requires mechanically yielding the airfoil in a secondary process. This secondary process is costly and it often produces inconsistent results. Consequently, it is desirable to combine the performance of the "twisted" blades with the economics of the uniform blades to achieve a high performance blade at a relatively low cost.
One attempt to achieve this result is disclosed in U.S. Pat. No. 4,618,313 to Mosiewicz. This patent discloses an axial propeller blade comprising a single tab (32) secured along its trailing edge. This single tab is also disclosed as being inclined from the blade at an angle of from 10.degree. to 70.degree. so as to enhance the lift of the blade. However, the tab of Mosiewicz is planar and of uniform or consistent configuration. Consequently, there is no possibility of this tab having one configuration and/or angle at the root end of the blade and another configuration and/or angle at the tip end of the blade so as to be more consistent with "twisted" blades. There is also no likelihood of this tab conforming to the multiple planes normally found in "twisted" fan blades which cause or result in increased performance.
Presently, there is no known fan blade which utilizes a multi-piece tab or fin that is either attached to or extruded from the trailing edge of a fan blade. Thus, it is an object of the present invention to provide a multiple piece fin which is extruded or attached to the trailing edge of the fan blade. Another object of this invention is to provide a fan blade incorporating a trailing fin whose angle and/or configuration can be varied as needed along the length of the fan blade for performance optimization. It is another object of this invention to provide a fan blade which is more economical to construct than "twisted" fan blades. Yet another object of this invention is to provide a fan blade whose operating performance is comparable with or exceeds that of "twisted" fan blade. These and other objects and advantages of this invention will become obvious upon further investigation